The present invention relates to a hydraulic impact tool for use in a well, such as an oil or gas well, in particular to apply impact energy to a stuck object in order to get the object loose or break it.
Impact tools are often used in connection with operations, in which valves, measuring equipment and other equipment is to be anchored down in a well. An impact tool is attached as an extension of a pipe string, for example a drill string or coiled tubing, and equipment to be placed in the well is attached to the free end of the impact tool. The impact tool has a channel extending therethrough, so that fluid may pass. The equipment to be set in the well, may be provided with grippers, resilient lugs or other things which engage grooves or seat surfaces provided in the wall of the well. To ensure that the equipment does not become detached, it is often provided with a locking device which is activated through the shearing of a shear pin. In some cases the pipe string cannot transfer sufficient mechanical force to break the shear pins, and the shear pins may then be broken by means of an impact tool. Also, the impact tool is often provided purely as a precaution to make it possible to get the equipment loose in case it should get stuck.
In a hydraulic impact tool a movable, maybe sleeve-shaped hammer is biased towards a stop by means of an outer spring. A stroke is made by displacing the hammer from the stop, and then let the pre-tensioned spring drive the hammer back to the stop.
The hammer has a hydraulic piston arranged thereto, provided with a through passage in which a valve is provided. The valve is normally open, so that fluid may pass through the piston. By activating the valve and closing the through passage, the piston is displaced, and thereby the hammer is displaced from the stop when pressurized fluid is applied to it. At the same time the spring is further tensioned because of the movement of the hammer.
As the hammer reaches an end position, the valve is opened, so that fluid again may flow through the piston. The hydraulic force against the piston then quickly drops, and the spring drives the hammer (with the piston) back towards the stop. The valve is activated and then again closes the through passage in the piston, and the process is repeated.